The invention relates generally to wireless communication systems and services and more particularly to Multiple Input Multiple Output (MIMO) technology applied to Distributed Antenna Systems (DAS).
An internal wireless communication system is often deployed to overcome coverage problems inside buildings. The most commonly used internal coverage system is a Distributed Antenna System in which multiple antennas are distributed in the building to provide the required coverage. The antennas are connected, directly or indirectly, to a radio source through coaxial (“coax”) cables. The DAS can provide a multiplicity of wireless services in a variety of frequency bands. Since each wireless service is operated in a distinct frequency band, the services do not interfere with each other when they are propagated through the coaxial cables. Using such an architecture, it is possible to provide a multiplicity of services to each antenna of a DAS via a single coaxial cable, while the feeding point is located remotely in a service closet or in a communication room.
An exemplary known DAS is shown in FIG. 1. Three services (Service A, Service B and Service C) are connected to a service combiner 102. The signals of the services are combined in a way that each coaxial cable 104 carries the three services. Since the services are in different frequency bands, they can be distributed on the same cable without disturbing each other. The cables connect the service combiner to antennas located in locations 1 to 4 chosen to provide optimal coverage to the covered area.
The emergence of the MIMO technology has changed the situation. MIMO technology is based on reception and transmission of signals that share the same spectrum, through two or more co-located antennas. That is, MIMO is a technology in which each antenna location includes multiple antennas that process different data streams at the same frequency.
One problem with trying to implement DAS architectures with MIMO technology is the requirement to route each of the MIMO signals in a separate coaxial cable to avoid mutual interference between the signals. This may result in significant increase in the amount of coaxial cables required and may significantly increase the cost and complexity of the installation.
Therefore, there is a need for and it would be advantageous to have systems and methods that supporting implementation of MIMO technology with a “conventional” DAS architecture, i.e. the use of a single coaxial cable.